Abstract

Experimental carbonate cementation under various conditions of temperature, solution composition and physical environment of cementation resulted in cements analogous to their natural counterparts reported in the literature. Scanning electron microscopic (SEM), optical microscopic, and chemical analyses of these experimental cements confirm and provide additional criteria for distinction between cements formed 1) in NaCl fresh and marine waters, 2) at various temperatures, and 3) in phreatic and vadose environments. The morphology of a cement crystal is a function of the growth rates of its various faces and of variation of these rates with time. Growth rate is dependent on nucleation rate, temperature, supersaturation state, crystal structure, and presence of various ions in solution. These factors are not necessarily independent. In our experiments the morphology of the cement crystals formed in fresh water did not differ significantly from those formed from NaCl solution except in size, whereas, cement crystals precipitated in the presence of Mg (super ++) ion were morphologically different from those obtained from the other solution compositions. Crystal size varies directly with temperature, supersaturation, and NaCl content of the solution. Increasing temperature and NaCl content of a solution appear to result in increasing crystal size of calcite cements. Three-sided pyramidal crystals of calcite formed in salt- and fresh waters are exact replicates of Mg-calcite cement reported from marine environments, indicating that the composition of the cement may not be inferred from morphology alone.

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